The invention relates to the transfer of packet-switched data in a system comprising a mobile terminal, a wireless local network and a mobile network.
Packet-switched data transmission services have been developed for mobile terminals. GPRS services (General Packet Radio Service) are widely used in terminals supporting the GSM radio technology and packet-switched services of the 3GPP system (Third-Generation Partnership Project) based on the WCDMA (Wideband Code Division Multiple Access) radio technology are also based on GPRS. PDP contexts are generally logical connections on which IP data are transferred from a mobile station to a boundary node (GGSN) in a GPRS/3GPP network and vice versa. Different PDP contexts may be provided with different quality of service (QoS) properties, thereby enabling optimal transmission of time-critical or error-critical data, for instance. In addition, an IP multimedia subsystem IMS is designed in the 3GPP system for providing various IP multimedia services to 3GPP mobile stations (UE; User Equipment). The IMS utilizes PDP contexts for data transfer to or from a mobile station. The IMS includes functions that enable the negotiation of an end-to-end session on the application plane using the SIP protocol (Session Initiation Protocol), the features of the session being for instance the codecs used, the termination points and the quality of service (QoS). For arranging the negotiated end-to-end quality of service also in the 3GPP network, a service based local policy (SBLP) is applied. The IMS includes a call session control function (CSCF), which includes a PDF function (Policy Decision Function) for authorizing quality of service resources (bandwidth, delay, etc.) for an IMS session based on SIP-layer SDP information (Session Description Protocol).
Besides access via the conventional access networks of the PLMN (Public Land Mobile Network) networks, such as the BSS (Base Station Sub-system) of the GSM, a need has also risen to allow access to the services of a PLMN by local networks primarily targeted at providing high speed data transmission in a limited area, such as in an office building. WLAN (Wireless Local Area Network) technologies are very popular today and standardization work has been done in 3GPP to define WLAN-3GPP interworking. This interworking may include the usage of 3GPP subscriber management procedures, such as authentication and charging procedures, as well as data transmission via the 3GPP core network for mobile terminals in a WLAN network. The basic concept is to provide a 3GPP subscriber with access via a WLAN network, also when roaming abroad. 3GPP specification TS 23.234 “3GPP system to Wireless Local Area Network (WLAN) interworking”, version 6.0.0, March 2004, defines the system description for WLAN-3GPP interworking.
For WLAN interworking, the 3GPP network is provided with some new network elements or entities. A WLAN Access Gateway (WAG) is a gateway via which the data to/from the WLAN Access Network is transferred to provide the MS with 3G PS based services. A Packet Data Gateway (PDG) is a network element providing access for WLAN roaming mobile terminals to external IP networks, including those supporting 3GPP PS (Packet-switched) domain-based services. An AAA (Authentication, Authorization and Accounting) server may provide authentication and charging services for WLAN roaming mobile terminals.
It is desirable that end-to-end QoS negotiation also be provided for mobile terminals roaming in WLAN networks. The above-mentioned 3GPP specification TS 23.234 defines on page 29 that the PDG performs the functions of a service-based local policy enforcement point (PEP) and communicates with a policy decision function to allow a service-based local policy. QoS interworking information may be obtained from the policy decision function. IETF RFC (Request For Comments) 2753 “A Framework for Policy-based Admission Control”, R. Yavatkar et al., January 2000, describes a framework for providing policy-based control and a client-server protocol for communication between a policy server (PDP; Policy Decision Point) and its client (PEP). However, the 3GPP specification TS 23.234 does not disclose how to arrange the adoption of the policy for the terminal in the WLAN-3GPP interworking system.